Thermostructural composite materials are characterized by their mechanical properties that make them suitable for constituting structural elements and by their ability to conserve their mechanical properties at high temperatures. Typical thermostructural composite materials are carbon-carbon (C--C) composites and ceramic matrix composite (CMC) materials.
C--C composites are constituted by a reinforcing texture or "preform" of carbon fibers that is densified by a matrix of carbon. CMCs are constituted by a preform of refractory fibers (carbon fibers or ceramic fibers) densified by a ceramic matrix. A ceramic material commonly used for manufacturing CMCs is silicon carbide (SIC).
The preform of a C--C composite or of a CMC is made by stacking or draping unidirectional plies (sheets of mutually parallel yarns or cables) or multidirectional plies (pieces of woven cloth, webs of fibers, pieces of felt), or by winding yarns, tapes, or strips, or by three-dimensional weaving. When draping plies, they may be bonded together by needling, by sewing, or by implanting transverse threads. Preforms are made of ceramic or carbon fibers, or more generally of fibers made of a precursor of ceramic or carbon, with the precursor then being transformed after the textile operations required for manufacturing the preform have been completed.
The purpose of densifying a preform is to fill the accessible pores thereof with the matrix-forming material. Such densification can be implemented by impregnating the preform with a liquid that contains a precursor of the matrix material and then transforming the precursor, or by chemical vapor infiltration.
The techniques mentioned above for making fiber preforms out of carbon or ceramic, and for densifying them by means of a carbon matrix or a ceramic matrix are well known.